Characterization of Fuel Composition Effects in H₂/CO/CH₄ Mixtures Upon Lean Blowout

This paper describes measurements of the dependence of lean blowout limits upon fuel composition for H₂/CO/CH₄ mixtures. Blowout limits were obtained at fixed approach flow velocity, reactant temperature, and combustor pressure at several conditions up to 4.4 atm and 470 K inlet reactants temperature. Consistent with prior studies, these results indicate that the percentage of H₂ in the fuel dominates the mixture blowoff characteristics. That is, flames can be stabilized at lower equivalence ratios, adiabatic flame temperatures, and laminar flame speeds with increasing H₂ percentage. Various methods of correlating these data were evaluated, using combinations of Lewis number (Le_mix), adiabatic flame temperature (T_ad), flame speed (S_L), and chemical time (τ_chem). These correlations clearly indicate the significance of the mixture diffusivity, heat content, and flame propagation speed upon blowout characteristics across a wide fuel spectrum. Two basic models of flame stabilization discussed in the literature were evaluated — a well-stirred reactor based approach that considers the ratio of chemical and flow times, and a propagative mechanism that considers the ratio of flame and flow speed. Both mechanisms were able to correlate some, but not all segments of the data set.